1. Field of the Invention
This invention relates in general to sliders for magnetic thin film heads, and more particularly, to sliders for magnetic thin film heads having a silicon coating formed over the air bearing surface thereof.
2. Description of Related Art
Magnetic disk devices have been in widespread use and are popular as external storage. A magnetic disk device includes a magnetic disk, a motor for rotating the magnetic disk, a slider radially movable along the magnetic disk, and a magnetic head mounted on the slider to perform data read and write operations with respect to the magnetic disk.
Achieving higher recording densities has required a reduction in the separation between the head and the surface of the magnetic disk. Storage systems in use commercially today use a slider that rides on a hydrodynamic air bearing during normal operation. The disk is typically coated with a lubricant, such as perfluoropolyether (PFPE), to prevent wear to the disk and slider during contact start and stop maneuvers and occasional asperity contacts. Two primary recording concepts are currently being used: true contact and near-contact recording. True contact recording uses very small sliders coated with low wear rate materials that are allowed to slide directly against the disk. In near-contact recording, a liquid bearing surface or an air bearing surface is used to separate the head from the disk.
Nevertheless, with either recording concept, the slider may rest upon the surface of the magnetic disk when not in use. During information retrieval and recording, however, the magnetic disk is rotated. When the disk first begins rotating, the slider slides along the surface of the magnetic disk. With near-contact recording, as the rotational speed of the disk increases, a boundary layer of air is formed which causes the slider to lift off of the disk and "fly" above the surface of the disk. When the power to the disk drive is once again shut off, the disk rotational speed gradually decreases, and the slider lands upon the disk, sliding along the surface of the disk until the disk comes to rest.
Several problems arise from the contact of the slider with the disk. With respect to both types of recording systems, the slider may be sliding directly in contact with the disk surface during start up and slow down of the disk. This frictional contact causes wear of the disk and slider. The excessive wear on the disk reduces the effective useful life of the disk.
Furthermore, even with near-contact recording systems, contact between the slider and disk also may occur when the disk is at full rotational speed. Although the boundary layer of air normally acts to support the slider above the disk, high points (asperities) on the otherwise smooth surface of the disk at times cause the slider to make contact with these projections on the disk. When the slider impacts these asperities on the disk, the slider often gouges the disk surface, further degrading the disk surface, as well as causing damage to the head and slider.
Accordingly, there is a need to protect the slider and disk surface from damage, namely by depositing a final layer at the air bearing surface in the fabrication of magnetic thin film heads. This surface provides a durable interface between the head and disk during file operation. Another function of the final layer is to provide a surface on which the flyheight can be measured, e.g. a surface with simple and consistent optical properties. In order to provide a durable interface, a low friction, durable and mechanically tough coating is required. In order to provide surface conducive to fly height measurements, an optically reflective, single layer material is required. Many materials, such as SiN, SiC, TiN, DLC, TiW etc. have been tried. Nevertheless, all such materials have failed either by the first or second criteria. For example, in the case of a silicon slider, the coating is not identical to the silicon slider body, which creates thermal mismatches and mechanical stresses. Thus, a stable slider dimension (crown, camber, pitch, etc.) can not be maintained with the temperature excursion encountered by the file.
To overcome the head disk interface durability problem with metallic layers such as TiW, a thin and durable hydrogenated carbon overcoat has been applied as the final step in head fabrication.
U.S. Pat. No. 5,159,508 to Grill, et al., and U.S. Pat. No. 5,175,658 to Chang et al., both of which are incorporated by reference herein, describe the use of a DC biased substrate in an RF plasma deposition apparatus to deposit an adhesion layer and a thin layer of carbon upon the air bearing surface of a slider. These references describe depositing an adhesion layer to a thickness of between 10 and 50 Angstroms (i.e., 1 to 5 nm), and a carbon layer to a thickness of 50-1000 Angstroms (i.e., 5 to 100 nm) upon the flat surface of a slider. An etching technique is then used to form a patterned area, which includes rails, on the air bearing surface. A solvent is then used to remove the photoresist layer which is used to control the etching.
These methods suffer from several disadvantages. Primarily, the Grill and Chang references disclose a method by which the protective coating (plus a masking layer as described in the Chang reference), is placed to protect the slider. These layers are necessary to protect the slider during subsequent etching which is done to form the patterned air bearing surface, and for subsequent solvent removal of the photoresist layer after etching.
Unfortunately, this method requires the placement of a substantial thickness of coating across the entire slider so that the sensor will not be damaged during the etching process. Further, this method does not allow control over the depth of the coating material across the air bearing surface of the slider. In particular, during the etching and solvent removal steps, which are done to form the patterned surface in the slider and to remove a photoresist material, the coating is removed in an uncontrolled fashion This causes the coating thickness to vary across the air bearing surface of the slider.
A further problem with this method is that the magnetic spacing is increased by the thickness of this carbon overcoat. This increase in magnetic spacing is significant in the low flying height file because it can occupy as much as 50% of the total spacing and degrade the file performance.
Thus it can be seen that there is a need for overcoat material, which has the better combination of durability and optical properties compared to TiW.
It also can be seen that there is a need for an overcoat material that is compatible with different slider body materials such as silicon which imposes little concern about the thermal expansion and mechanical stress effects on the slider.
It can also be seen then that there is a need for an overcoat material that does not create magnetic spacing loss.